PhD Defense: Sampo Saarinen

Optomechanics at the room temperature - Towards classical and quantum applications

The field of optomechanics concerns interaction between mechanical motion and electromagnetic radiation. The interaction allows for exceptionally precise measurement of the motion and control of mechanical motion on the level of a single quantum. In the recent decades, steady progress in fabrication techniques has enabled increasing number of experiments probing fundamental quantum mechanics. On the other hand, the optomechanical interaction promises new applications in force sensing, detection of electromagnetic fields and as a platform for budding quantum networks. We present two room temperature experiments as steps towards such technologies.
First, we have developed an integrated opto-electromechanical transducer for use in clinical MRI machines. The device integrates an optical optical cavity and electrodes on a single chip and is fiber coupled. An aluminium membrane forms one half of a parallel plate capacitor and one mirror of a Fabry-Pérot-cavity. The device is connected to a resonant electrical detection circuit and we infer the noise temperature of the transducer device tobe 210 K. In a proof of principle experiment, we image an MRI phantom in a commercial 3 T MRI scanner.
Second, we have built an optical cavity consisting of a fiber mirror and a phononic crystal mirror exhibiting low phase noise. Combined with a soft-clamped silicon nitride membrane, the optomechanical system can reach quantum cooperativity greater than one. We further feedback cool the resonators mode from room temperature to an occupation of n = 20 phonons. The final occupation is limited by poor detection efficiency caused by suboptimal mode matching.